1. Field of the Invention
The present invention relates to a load control mechanism for an internal combustion engine, which is disposed in the internal combustion engine and structured to partially return an exhaust gas discharged into an exhaust passage to a combustion chamber.
2. Description of Background Art
An internal combustion engine provided with an exhaust gas recirculation (EGR) device for partially returning the exhaust gas to the combustion chamber is known. The internal combustion engine of the aforementioned type has an advantage wherein the a low NOx content of the exhaust gas occurs as compared with the internal combustion engine with no EGR device.
An internal combustion engine normally requires a high fuel consumption rate (hereinafter also referred to as “fuel efficiency”). JP-A No. 2006-233963 discloses the art of introducing the exhaust gas (combusted gas) during the open state of the exhaust valve.
In the internal combustion engine, the amount of intake air to the combustion chamber is adjusted in accordance with the opening degree of the throttle valve. For example, the intake air amount is reduced by decreasing the opening degree of the throttle valve.
In the aforementioned case, as the opening degree of the throttle valve is reduced, the area of the passage which allows the air flow is also reduced. The intake resistance is then raised to generate the so-called pumping loss (see FIG. 5).
The use of the direct-injection stratified-charge engine may be considered for avoiding generation of the pumping loss. In this case, the inside of the combustion chamber is kept substantially at the atmospheric pressure in the intake stroke as shown in FIG. 6, thus avoiding the increase in the pumping loss.
However, in the direct-injection stratified-charge engine, a special mixture gas has to be formed, and the structure is inevitably complicated for the purpose of directly injecting the mixture gas into the combustion chamber. The combustion chamber is further required to be specifically configured to satisfy the aforementioned condition. The atomization of the mixture gas is required to be under strict control. As the exhaust gas contains surplus oxygen by relatively larger amount, the post processing of the NOx has to be considered as well.
The use of the engine with variable intake valve closing time for lean-burn combustion has also been considered as another way for suppressing the pumping loss. However, the capability of the lean-burn combustion for suppressing the pumping loss is limited. The engine with variable intake valve closing time further requires the variable valve mechanism with improved responsiveness and mechanical efficiency.